The present invention relates generally to systems for detecting flaws in optical fibers and, more particularly, to a system and method for detecting flaws and for identifying the types of flaws in an optical fiber wherein a beam of collimated light rays illuminates the optical fiber and is acted upon to form a plane when a flawless optical fiber is illuminated. Portions of the beam which are scattered outside of the plane by flaws are monitored to detect and identify those flaws.
Due to their excellent transmission characteristics, optical fibers are being increasingly used as signal carriers not only in communications systems but also in a wide variety of other applications including weapon systems and medical diagnostic instruments. Generally, optical fibers consist of a fiber core surrounded by a fiber cladding which has a lower index of refraction than the fiber core. Within the layers of an optical fiber, nonuniformities may occur as a result of faulty fabrication or improper handling of the fiber. The nonuniformities may include, for example, bubbles, lumps, neckdowns, coating defects, surface contamination, core contamination and the like.
Such nonuniformities may increase the signal losses in the fiber or, in the extreme, completely terminate signal transmission. It is apparent that these deleterious effects of defects or flaws in the optical fiber may result in malfunction of a device in which the fiber is employed. Consequently, optical fibers must be carefully examined to detect and identify any such defects or flaws.
Fiber optic flaw detection systems which direct a laser beam toward an optical fiber and monitor the refraction and diffraction of the laser beam to detect flaws are known in the art. For example, U.S. Pat. No. 4,924,087 issued to Bailey et al. discloses a fiber optic defect detection system wherein the optical fiber to be examined is extended axially through a dish-like structure and illuminated by one or more laser beams directed substantially orthogonal to the fiber axis. For a flaw free optical fiber, the laser beam is scattered by the optical fiber onto a light-absorbing band on an inner surface of the dish as in-plane scattered rays. For an optical fiber having a flaw, a portion of the laser beam is scattered outside the band as out-of-plane scattered rays. Out-of-plane rays which deviate a sufficient amount from the band illuminate an aperture located above the band and are detected as flaws.
Unfortunately, the Bailey et al. flaw detector does not respond to out-of-plane light rays which are scattered below the light-absorbing band such that this detector is at best not as sensitive as possible when detecting flaws which only cause such scattering or predominately scatter rays in that direction. Furthermore, the Bailey et al. flaw detector does not identify the type of flaw, lump or neckdown, which is detected.
U.S. Pat. No. 4,021,217 issued to Bondybey et al. discloses a method for detecting optical fiber defects wherein the off axis scattering of a beam of monochromatic light by the optical fiber is monitored to detect defects. A plurality of light detectors detect the amount of off-axis light diffracted by flaws in the optical fiber and generate signals representative of the flaws. The magnitudes of the generated signals provide an indication of the sizes of detected flaws. However, the Bondybey et al. flaw detector does not distinguish between, for example, a lump or a neckdown, in the optical fiber.
Identifying the type of flaw in an optical fiber can be beneficial in a variety of circumstances. Such information may be of great importance, for instance, to a manufacturer of optical fibers. The manufacturer may correct a defective manufacturing process based partially on the type of flaws present in the optical fiber. Thus, early detection and identification of flaws in the optical fiber may provide invaluable assistance to the manufacturer in correcting the manufacturing process.
Accordingly, a need exists in the art for an improved approach to flaw detection and identification in optical fibers which is fast and reliable, accurately detects flaws, identifies the types of flaws, such as lump or neckdown, and is easy to operate.